The present invention is directed to ink-jet printable media and more specifically to ink-jet printable media having an absorptive substrate, a ink-vehicle permeable coating, which may have been radiation cured, overlying the substrate and a microporous ink-receptive coating overlying the ink-vehicle permeable coating.
Ink-jet printing systems are highly effective for producing colored images on various substrates, such as papers, films, and other imaging media, that can be used in different applications. For example, ink-jet printed media have found many commercial uses for indoor and outdoor signage, posters, bulletins, advertising banners, and the like where vendors are looking to provide colorful graphic displays. Modern ink-jet printing systems employ various digital technologies, inks, and ink-jet printers to produce high-quality printed images on the imaging media.
In a typical ink-jet recording or printing system, ink droplets are ejected from a nozzle at high speed toward an imaging media to produce an image. The ink droplets generally comprise a recording agent, such as a dye or pigment, and a liquid vehicle. The vehicle can be made up of water, an organic material such as an alcohol and various other additives.
Inks used in ink-jet printers can be dye-based, pigment-based or a combination. In dye-based inks, the colorant (dye) is molecularly dispersed or solvated by a carrier medium. In pigment-based inks, the colorant exists as discrete particles. Some inks comprise both pigments and dyes.
The ink-jet imaging media generally comprises a substrate and an ink-receptive layer formed on an imaging surface of the substrate. The substrate can be selected from a wide variety of materials such as papers, films, non-woven webs, metal foils, and the like. This substrate is then coated with specially formulated ink-receptive compositions that are capable of receiving and holding the aqueous-based inks effectively so as to generate a quality printed image. Various surface finishes, such as matte, satin and gloss finishes can be achieved by proper selection of suitable substrate materials and coating compositions.
While the earliest forms of ink-jet media were a significant improvement over the use of plain paper, the ink-jet media industry has continuously strived to develop coated ink-jet media products capable of recording printed images having improved color brilliance, resolution, and density as well as other desirable properties. For example, one goal is to provide ink-jet media that resists fading of the ink under high ozone conditions. Ozone-fade resistance is a particularly desirable feature for ink-jet imaging media used in outdoor applications.
Generally speaking, all ink-jet imaging media should be capable of absorbing the ink quickly so that the printed image dries instantaneously or within a very short period of time but yet should have good water-resistance (i.e., the printed image should have good resistance to being smeared or rubbed off when the image is wetted.) Another common industry objective is to provide imaging media having at least a satin, and preferably, a glossy surface finish.
In recent years, the ink-jet industry has attempted to address the need for imaging media having improved print properties by developing ink-receptive coatings that commonly are referred to as “microporous” ink-receptive coatings. These microporous ink-receptive coatings contain particles and polymer binders. The particle and polymer binder materials, in combination, provide the ink-receptive coating with a microporous morphology that can better absorb aqueous inks.
Although ink-jet imaging media coated with microporous ink-receptive coatings have some advantageous properties and can effectively record high-quality images, in certain instances, some of these products can also have certain drawbacks.
Cracking of the microporous coating is one issue. For example, where a relatively high surface gloss, i.e. a gloss reading of 40 or more, is desired, it is often required to deposit a relatively thick layer of the microporous coating onto the underlying substrate (such as a paper substrate with a matte surface). The thick microporous coating will adequately receive the inks to form the printed image, but it is prone to developing small cracks during the manufacturing process. These coatings are typically applied to rolls of a substrate traveling in a continuous coating process. The substrate is coated and then passed through a drying tunnel to dry the coating before the next coating process. Thicker coatings require longer drying times, longer drying ovens and thus more manufacturing time and expense. Accelerating the drying process to reduce costs and manufacturing time tends to cause the coating to crack.
Thick coatings of the microporous material can also cause a change in color hue of the printed image. In some instances, composite colors contained in the printed image, which are produced by certain inks, do not appear as the intended color on the microporous coated layer. For instance, cyan (C), magenta (M), and yellow (Y) inks may be selected and applied to the medium in order to produce a composite black color, but the actual printed color may be a dark blue. It is believed that multiple scattering of the light within the microporous coating causes this color shift.
Finally, cost is another issue. The microporous coating materials are relatively expensive, and applying thick coats of the microporous material is expensive, driving up the price of these coated media.
It has been suggested that a radiation-cured polymer barrier coating, applied to the base substrate beneath the microporous coating, can lead to a glossy medium. See U.S. Pat. No. 6,610,388. However, because that radiation-cured coating forms a moisture barrier and thus is not permeable, the aqueous ink vehicle must be absorbed entirely within the microporous top coating. The microporous coating in that configuration does not need to be very thick to provide gloss, but it still needs to be thick enough to absorb all the aqueous ink vehicle. Accordingly, there is a trade-off between reducing the thickness of the microporous coating material enough to reduce its cost and cracking during manufacture, on the one hand, and increasing it to achieve good gloss and good drying characteristics, on the other.
There is thus a continuing need in the industry for improved ink-jet imaging media that has a relatively high gloss and superior printing characteristics, but yet does not require the application of a thick microporous ink-receptive layer.